U-value Calculations

Cross-Sectional Areas of Wall Ties for U-value Calculations

For the accurate calculation of U-values for walls it is important to use the correct information for stainless steel wall ties.

Using the actual cross-sectional area and the thermal conductivity value of a tie, rather than allowing a program to apply a default value, can make a considerable difference to the calculated U-value. It is widely accepted that default values for wall ties over-estimate the thermal bridging effect.

The required information for the main Ancon and Staifix wall ties are shown in the table below.The Ancon TeploTie / Teplo-BF is manufactured from pultruded basalt fibres set in a resin matrix. These ties have a thermal conductivity of just 0.7W/mK.

Fixings with a lambda value of less than 1.0W/mK are excluded from u-value calculations to BS EN ISO 6946, so TeploTies are always excluded irrespective of their cross-sectional area.

Chi values are available for the Ancon Teplo-L-Tie which has a basalt fibre body and a stainless steel upstand for surface-fixing.

Ancon and Staifix stainless steel wall ties have a thermal conductivity of 17W/mK. They are value-engineered; all unnecessary material is removed to minimise the thermal bridging effect.

Ancon Tie Reference

Tie Length (mm)

Cavity Width (mm)

Wall Tie Type*

Area (mm2)

HRT4

200

50-75

4

3.5

HRT4

225

76-100

4

4.2

HRT4

250

101-125

4

6.2

HRT4

275

126-150

4

6.2

RT2

200

50-75

2

8.6

RT2

225

76-100

2

8.6

RT2

250

101-125

2

8.6

RT2

275

126-150

2

10.2

DT (Double Triangle)

200

50-75

2

7.5

DT (Double Triangle)

225

76-100

2

7.5

DT (Double Triangle)

250

101-125

3

7.5

DT (Double Triangle)

300

150-175

3

8.6

ST1

200

50-75

1

19.5

ST1

225

76-100

1

19.5

ST1

250

101-125

1

19.5

ST1

275

126-150

1

23.4

ST1

300

151-175

1

23.4

ST1

325**

176-200

1

23.4

ST1

350**

201-225

1

23.4

TJ2

205-305

50-150

Varies

8.8

STF50

127

50

6

12.0

STF75

152

75

6

12.0

STF100

179

100

6

12.0

TIM6

175-250

50-150

Varies

6.6

SDB/V

125-150

45-94

Varies

38.0

SDB/V

175-200

95-144

Varies

47.5

**Type 1 performance declared in M2 mortar only

Masonry-to-masonry wall ties are usually installed at 900mm horizontal centres and 450mm vertical centres; this is equivalent to 2.5 ties/m2. Timber frame are installed at closer centres which is equivalent to a density of 4.4 ties/m2.

With the Ancon 25/14 system, only the channel fixing screw passes through the insulation to create a thermal bridge; the channel and wall tie are located outside the insulation. Ancon’s stainless steel fixings screws, referenced HTSS, have a cross sectional area of 15.2mm2 and a thermal conductivity of 17W/mK. Ancon 25/14 channels are typically fixed at 600mm horizontal centres to suit steel layout and 337.5mm or 450mm vertical centres depending on insulation depth.

Separating (Party) Walls

Ties in separating walls should comply with Approved Document E.

U-value Calculations to BS EN ISO 6946

BS EN ISO 6946 permits the corrections due to wall ties, air gaps etc to be omitted if the corrections amount to less than 3% of the uncorrected U-value of the element.

U-value calculation programs either include a function to allow this 3% rule to be applied (e.g. BRE U-value calculator) or automatically apply it where necessary (e.g. BuildDesk U 3.4).

Ancon is pleased to announce that it has successfully transitioned its Quality and Environmental Management Systems to ISO 9001:2015 and ISO 14001:2015 respectively, well ahead of the September 2018 industry deadline.